The application of contemporary microscopy methods such as transmission electron microscopy, nanotomography, or the investigation of micromechanics-related aspects of materials often involves the preparation of three-dimensional samples with complex geometries. This can involve the removal of material volumes of a few tenths of a cubic micrometer (μm3) up to several tens of cubic millimeters (mm3). Given that in most cases only a specific portion of the object is of interest as a sample, one generally cannot arbitrarily select any region of the object for preparation as a sample. Rather, it is desirable to prepare a defined target structure out of the object in order to obtain the desired sample.
In the practice of transmission electron microscopy, so-called TEM lamellae are used which are transmittent to electrons. The length and width of the TEM lamellae are in most cases of the order of several microns (μm); their thickness in most cases is less than one hundred nanometers (nm). To ensure that TEM lamellae contain the desired targeted structure, they normally are prepared out of the full object material.
In nanotomography methods, the microscopy sample is cut away layer by layer, recording an image of each layer. The layer images obtained in this manner are then assembled into a three-dimensional reconstruction of the sample structure. In FIB/SEM tomography, the layers are removed via a focused ion beam (FIB), while the images of the layers are recorded with a scanning electron microscope (SEM). In addition, the elementary composition of the sample can be investigated via energy-dispersive X-ray spectroscopy (EDS), wherein the element-specific X-ray spectrum is analyzed which is emitted by the sample material in response to the incident electron beam.
As a further possibility, the samples can be investigated using wavelength-dispersive X-ray spectroscopy (WDS).
In samples that contain crystalline structures, the technique of electron backscatter diffraction (EBSD) can be used to investigate the distribution of the crystal orientations based on the back-scattered electrons. As a general principle for tomography samples, especially if the same sample is also to be used to perform EDS- or WDS analyses, the target volume first is set free within a larger material space in order to avoid unwanted obscuration- and/or redeposition effects. In the case of FIB/SEM tomography, samples are prepared in the shape of rectangular blocks which remain connected to the object along one of the shorter side surfaces or, alternatively, along one of the short surfaces and also at the base surface. Similar block-shaped samples are used for EBSD investigations. In this case, however, all of the object material on one side is removed, so that the sample block stands out into free space. For investigations with high-resolution X-ray tomography or synchrotron radiation tomography, needle-shaped samples are used. A needle-shaped sample in essence has the shape of a cone with a base diameter that is small in proportion to its height and with a long, pointed apex. While the needle-shaped sample rotates about its longitudinal axis, a plurality of images are recorded using conventional X-rays or synchrotron radiation and using suitable detectors, whereupon the recorded images can be assembled into a three-dimensional representation of the sample.
For an in-situ investigation of micromechanical material properties, one uses samples of specific geometric shapes, for example rod-shaped samples for use as bending beams, which have been prepared out of the full sample material. Cantilever beams, which are rigidly held at one end and free at the other, are for example well suited for the investigation of the elastic properties of a material. In experiments of this kind, the bending beam which measures in most cases only a few hundred microns in length is subjected to a controlled deformation which is simultaneously observed with the scanning electron microscope (SEM). With rod-shaped samples, the behavior of a material under tension or compression can be investigated with the scanning electron microscope by observing changes in the microscopic material structure under tensile or compressive loads.
Systems are known in which an electron microscope is used to investigate the sample and where the radiation beam generated by the electron microscope is also used to activate a process gas which is delivered to the sample, so that the activated process gas will modify the sample as material is removed or separated from the sample.
Also known are systems that include an electron microscope and an ion beam column whose radiation beams can be aimed simultaneously or alternatively at a location of a sample that is to be modified. Here, the ion beam serves to modify the sample while the progress of this process can be observed with the electron microscope. Additionally, it is possible in such a system to inject process gas in order to modify the sample through the process gas which is activated by the electron- or ion beam. In the in-situ lift-out method, the sample that is to be prepared is cut free by the focused ion beam and subsequently transferred to a suitable sample carrier by a micromanipulator.
Although sample preparation with an electron beam and/or an ion beam and/or an activated process gas can be performed with a high degree of precision, such systems have the disadvantage that this kind of preparation is very slow and not always successful. In a process where a large sample volume is to be removed, this procedure will take a relatively large amount of time. Also, especially with the in-situ lift-out method the operator desirably has experience and experimental skill.
It is also known that laser-machining systems, especially of the type working with solid state lasers, can be used for the cutting, removing, drilling, welding or soldering of materials. The state of the art further includes systems in which a laser beam serves to remove material from a sample that is normally of a size of at most a few millimeters. To perform this process, a laser beam of sufficient radiation energy, i.e. photon energy, is aimed at predetermined target locations of the object by way of a sensor device or scanning device. This is accomplished by setting the scanner sweep of the scanning device in accordance with coordinates of the target locations in a coordinate system of the scanning device.
Also known are machining systems that include a particle beam column to generate a targeted particle beam and a laser system to generate a targeted laser beam. The particle beam column can include an electron beam column and an ion beam column, wherein these particle beam columns can also be configured for example as an electron microscope or an ion microscope insofar as they include a secondary particle detector. The secondary particle detector can for example be an electron detector or an ion detector.
Furthermore, a laser-machining system has been described in which an object can be machined with a comparatively high level of precision, wherein a changeover of the object in process is possible between a machining operation in the laser-machining system and a machining operation and/or inspection in a further machining and/or inspection system such as for example a scanning electron microscope. To meet this purpose, an object holder has been proposed which carries markings that allow the accurate, and thus reproducible, positioning of the targeted sample location.
The following references may be considered relevant: DE 10 2008 045 336; U.S. Pat. No. 7,442,924; and DE 10 2010 008 296.